Cisco 300-640 Questions Answers

The thermal events are the strongest diagnostic indicator in the scenario and should direct troubleshooting toward the server's cooling environment before workload-level tuning . Excessive temperature can cause processor or accelerator thermal throttling, which directly produces intermittent performance degradation and latency spikes even when CPU, memory, GPU, and storage utilization otherwise appear normal.

Cisco's C-Series installation requirements emphasize correct airflow and specifically warn that obstructing server ventilation can cause overheating, higher fan speeds, and increased power consumption. Cisco's C885A M8 documentation, representative of modern AI-oriented UCS C-Series platforms, specifies twelve hot-swappable system fans for proper front-to-back cooling.

Therefore, the administrator should first inspect ambient temperature, cold-aisle/hot-aisle conditions, physical airflow, obstructions, and fan health. Any failed fan should be replaced promptly.

Option A is a sensible performance-analysis step when there is no stronger hardware fault indicator, but repeated thermal events make it secondary here. Storage inspection in option B is not supported by the symptoms. Option C focuses on power delivery, yet the event evidence specifically points toward thermal management rather than insufficient PSU capacity.

Troubleshooting should follow the fault evidence, beginning with the lowest-level physical condition that can explain the observed symptoms.

Study Guide Reference: AI Infrastructure Operations and Troubleshooting — UCS health monitoring, environmental faults, thermal conditions, and performance troubleshooting.

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Cisco's validated guidance for connecting VAST Data storage through an ACI fabric explicitly configures the RDMA storage class with Weighted Random Early Detection and Congestion Notification enabled . This makes option A directly consistent with Cisco's documented configuration.

In Cisco's VAST Data ACI design example, storage traffic arrives marked with DSCP 26 and is assigned to the Level2 QoS class. PFC is enabled for the corresponding no-drop DSCP, bandwidth is reserved for storage traffic, the congestion algorithm is configured as WRED, and congestion notification is enabled.

WRED and ECN-style congestion notification work together to detect developing queue pressure before buffers overflow. Rather than waiting for tail-drop conditions, the network can mark congestion-capable traffic so RoCEv2 endpoints reduce their transmission rates. PFC provides the complementary no-drop behavior when congestion becomes sufficiently severe.

Option B disables the required congestion signaling. Options C and D use Tail Drop, which Cisco's documented VAST RDMA storage class does not use. Tail Drop is instead shown in the same Cisco design for control-plane and ordinary traffic classes where lossless RDMA behavior is not required.

This configuration is therefore not merely a generic QoS preference; it directly follows Cisco's published ACI-to-VAST storage design.

Study Guide Reference: AI Infrastructure Deployment and Data Management — QoS, ECN/WRED, PFC, RDMA storage, and lossless fabric configuration.

Priority Flow Control is a foundational mechanism used to provide lossless Ethernet behavior for RoCEv2. PFC operates on individual Ethernet priorities and allows a congested receiver or switch to pause transmission for the affected priority while permitting traffic in other classes to continue. Cisco's AI networking guidance explicitly states that PFC is enabled for RoCEv2 traffic to prevent packet drops caused by congestion.

This characteristic is critical for RDMA workloads because packet loss can trigger retransmission behavior and significantly degrade GPU collective communication performance. In an AI backend fabric, RoCEv2 is normally placed in a no-drop QoS class with PFC configured for that traffic class. ECN is commonly used alongside PFC to provide proactive congestion signaling, but PFC is the mechanism that directly prevents loss when buffers approach critical utilization.

Traffic shaping in option A may moderate burst rates but does not establish lossless transport. A high DSCP marking in option C provides classification and forwarding preference, not loss prevention. Weighted fair queuing in option D allocates scheduling bandwidth but also does not guarantee that packets will not be discarded during congestion.

Study Guide Reference: 3.1.a Congestion control mechanisms — PFC, ECN, ETS; 3.1.b RoCE/RoCEv2; 3.1.c QoS.

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Cisco UCS X-Series Direct is specifically designed for edge, retail, remote-office, and branch-office environments that require the operational characteristics of UCS without deploying separate top-of-rack Fabric Interconnect appliances. It combines the UCS X9508 chassis with integrated UCS 9108 100G Fabric Interconnect modules and supports centralized management through Cisco Intersight.

The decisive requirement is 200 Gbps of unified fabric connectivity per compute node . Cisco documents that two UCS 9108 100G Fabric Interconnect modules provide a total of 200 Gbps per compute node. The solution can support up to eight compute nodes per chassis and is explicitly positioned for remote and branch-office deployments.

The S3260 is primarily a storage-intensive UCS platform and does not represent the required branch-oriented modular compute architecture. Unified Edge is purpose-built for edge locations, but the specific 200-Gbps-per-compute-node requirement aligns directly with X-Series Direct. The C885A M8 is a high-density rack server for GPU-intensive AI workloads rather than a chassis solution optimized for these branch deployment requirements.

Study Guide Reference: 2.0 AI Infrastructure Components and Architecture — 2.2 compute scalability and redundancy; 2.5 hybrid AI deployment.

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